1. Field of the Invention
The present invention relates to an apparatus for receiving packet stream, and particularly to a packet stream receiver capable of receiving a packet stream and making it to optimized data.
2. Description of the Related Art
An encoding/decoding technique for video medium such as a moving picture and audio mediums has been increasingly developed in recent years. This is because moving pictures with high quality have been developed and the amount of information has increased, and further because a wired or radio network has been developed and a desire for transmitting picture information through the network has been increased.
The encoding/decoding technique for moving picture requires high compression efficiency, high quality in decoding, and good transmission efficiency, because the moving picture has remarkably information size. There is a technique called H.264/AVC (Advanced video coding), which is recognized as the international standard of the encoding/decoding technique for moving picture which satisfies these desires (hereinafter, simply denoted as H.264), and this encoding/decoding technique for moving picture is disclosed in, for example, for example, IEEE TRANSACTION ON CIRCUIT AND SYSTEMS FOR VIDEO TECHNOLOGY, VOL. 13, No. 7, 2003, “Overview of the H.264/AVC Video Coding Standard”, Thomas Wiegand.
Also in a mobile digital broadcasting of ISBT-T (Integrated Service Digital Broadcasting-Terrestrical), H.264/AVC (Advanced video coding) standard is employed for a moving picture encoding method, MPEG-2 standard or AAC (Advanced-Audio-Coding) standard is also employed for an audio encoding method. In the encoding methods, encoding stream is multiplexed on packets of a transport stream (TS stream) and the transport stream (TS stream) is transmitted. In such transport stream (TS stream) transmission, if an error occurs during transmission and part of packets is lost, that is, if packet loss occurs, discontinuity occurs in an elementary stream (ES stream) extracted from the transport stream (TS stream). Since a decoder at a reception side does not detect a discontinuity and continuously decodes the ES stream, video and audio data is erroneously interpreted.
If the ES stream corresponds to H.264 stream, a picture quality is degraded due to the erroneous interpretation. If the ES stream corresponds to AAC stream, noise, i.e., abnormal noise is also produced due to the erroneous interpretation.
As described above, the erroneous interpretation on the video or audio data causes the video or audio data to generate erroneous decoded picture or audio different from normal picture or audio inherent in the video or audio data so that a picture or audio quality is remarkably degraded.
In general, the decoder can detect an occurrence of error, only when a syntax error is occurred. However, in a method of small redundancy encoding type, there is produced a large span between an error generating point and an error detection point so that degrade of a reproduction quality is relatively large.
Similarly, also in streaming using RTP (Real Time Protocol), there is a similar problem that part of packets is lost and data is degraded due to an erroneous interpretation.